Probing the Formation, Structure, and Reactivity of Zn(II), Ag(I), and Fe(II) Complexes with 2,2′:6′,2″-Terpyridine on Ag Nanoparticles Surfaces by Time Evolution of SERS Spectra, Factor Analysis, and DFT Calculations

Abstract

The adsorption and surface reactivity of 2,2′:6′,2″-terpyridine (tpy) and its metal (M = Zn2+, Fe2+, Ag+) complexes on Ag nanoparticle surfaces together with the structure of the resulting Ms X+-tpy surface species and the mechanism of their formation have been investigated. The process was elucidated by time-dependent surface-enhanced Raman scattering (SERS) spectra, their treatment by factor analysis (FA), density functional theory (DFT) calculations of Raman spectra, and comparison of the SERS spectra of the surface species (obtained by FA) with the Raman spectra of their synthetic analogues (characterized by X-ray diffraction). SERS spectral time evolution revealed surface-induced decomposition of the [Zn­(tpy)2]2+ complex and formation of Zns 2+-tpy and Ags +-tpy surface species, accompanied by a ligand exchange of one tpy ligand for chloride anions on the Zn2+ center. The inhibition of Ags +-tpy surface species formation was achieved by addition of Zn2+ cations prior to the addition of the [Zn­(tpy)2]2+ complex. The [Fe­(tpy)2]2+ complex exhibited no surface decomposition and was identical to the Fes 2+-tpy surface species. Additionally, generation of Ms X+-tpy species on the Ag nanoparticle surfaces by reaction of tpy and M x+ cations was monitored by SERS and evaluated by FA. Determination of the Zns 2+-tpy and Ags +-tpy structures was supported by DFT calculations of the Raman spectra of Zn-tpy and Ag-tpy fragments.

Plasmon-catalysed decarboxylation of dicarboxybipyridine ligands in Ru(ii) complexes chemisorbed on Ag nanoparticles: conditions, proposed mechanism and role of Ag(0) adsorption sites

“…32 Furthermore, adsorbed chlorides were shown to provide Cl ligands for the tpy/2Cl ligand exchange undergone by Zn(tpy) 2 (tpy = 2,2′:6′,2′′-terpyridine) complex dication on Ag NP surfaces. 19…”

“…Both types of reactions have their analogues in the previously reported studies of surface reactivity of transition metal complexes. 19,32 In particular, decarboxylation of the dcbpy ligands in Ru(II)(dcbpy) 2 (SCN) 2 complex has been reported and proposed to proceed by plasmon catalysis. 32 Furthermore, adsorbed chlorides were shown to provide Cl ligands for the tpy/2Cl ligand exchange undergone by Zn(tpy) 2 (tpy = 2,2 0 :6 0 ,2 00terpyridine) complex dication on Ag NP surfaces.…”

“…32 Furthermore, adsorbed chlorides were shown to provide Cl ligands for the tpy/2Cl ligand exchange undergone by Zn(tpy) 2 (tpy = 2,2 0 :6 0 ,2 00terpyridine) complex dication on Ag NP surfaces. 19 Concerning this second, ligand exchange reaction pathway for Ru(bpy) 2 (dcbpy) chemisorbed on Ag NP surfaces, chlorides (or other ligands suitable for the ligand exchange) are, indeed, required as co-reactants. On the other hand, the relationship between the presence of chlorides and the progress of a decarboxylation reaction is, on the first sight, not obvious.…”

“…[14][15][16] Furthermore, detailed SERS and/or SERRS spectral studies carried out under various conditions can actually reveal new surface reactions undergone by chemical species. [17][18][19] Chromophoric Ru(II) polypyridine complexes are well known for their interesting photophysical properties 20 and as a class of efficient sensitizers in dye-sensitized solar cells. [21][22][23] These complexes have also been employed as model chromophores in exploration of the mechanisms of SERS and SERRS.…”

“…14–16 Furthermore, detailed SERS and/or SERRS spectral studies carried out under various conditions can actually reveal new surface reactions undergone by chemical species. 17–19…”